Microwave frequency dielectric properties of hexagonal perovskites in the Ba5Ta4O15–BaTiO3 system

The dielectric properties of the hexagonal perovskites Ba8Ta4+0.8xTi3−xO24 (x = 0, 0.4, and 0.8), Ba10Ta8−0.8xTixO30 (x = 0.6, 0.9, and 1.2) and Ba5Sr2Ta4ZrO21 were studied at microwave frequencies. XRD analysis did not reveal the presence of impurity phases in the obtained samples and the lattice parameters of solid solutions were linearly dependent on composition. These systems show a relatively high permittivity (27 < ɛ < 44) with a low dielectric loss (10,000 < Q × f < 31,000 GHz). Solid solutions Ba10Ta8−0.8xTixO30 with disordered face-sharing octahedra show higher Q × f values compared to ordered Ba8Ta4+0.8xTi3−xO24 compounds. Filling of empty vacancy layers by multicharged cations in the Ba5(Ta, Ti)4+δO15 system (0 < δ < 1) along with Ba5Sr2Ta4ZrO21 intergrowth leads to decrease a quality factor. The effect of increasing Ti content in the pseudobinary Ba5Ta4O15–BaTiO3 system on microwave dielectric properties is discussed.